Congenital hemolytic anemias include a heterogenous group of intrinsic red cell abnormalities that are sometimes classified as disorders of hemoglobin (hemoglobinopathies and thalassemia syndromes), red cell enzyme-deficiency disorders, and abnormalities of the red cell membrane and cytoskeleton. In patients affected with any of these conditions, red cell transfusions may be indicated to compensate for the decreased oxygen-carrying capacity associated with the underlying anemia. Furthermore, red cell transfusions may also be indicated for pathophysiological consequences unique to each of these disorders. It may therefore be desirable to transfuse patients with a red cell preparation.
Red blood cells are the type of transfusion normally associated with blood transfusion. Its primary purpose concerns oxygen transfer--hemoglobin in the red cells transfers oxygen in the lungs to tissues in other parts of the body.
A typical unit of whole blood includes about 450 ml of whole blood and about 65 ml of anti-coagulant. Thus a unit of whole blood typically includes a hematocrit of about 36% to about 44%. Hematocrit typically refers to the proportion of erythrocytes in blood. A method of measuring the hematocrit may be by dividing the volume of packed erythrocytes by the volume of the specimen, and multiplying by 100.
Whole blood may be separated into its components for use in transfusions. For example, red blood cells may be prepared as a component by removing approximately 200-250 ml of plasma. This red cell component is typically referred to as packed red cells (PRC), the hematocrit of which is typically in the range from about 52% to about 60% when additives are used, and about 70% to 80% when no additives are used. Under typical storage protocols, the hematocrit of stored PRC must be maintained from about 60% to about 70% in order to retain or assure viability of the red cells. Saline washed red cells are typically prepared using automated equipment for removal of plasma, with the usual final hematocrit in the range from about 70% to 80%.
It has now been shown that it may be desirable to transfuse a red cell product having a high hemoglobin content (i.e., high hematocrit, typically above about 80%) to increase the amount of oxygen-carrying capacity in the patient. Because high hematocrit packed red cells are typically not administered, the focus in the development of leucocyte depletion devices has been on normal hematocrit red cell containing solutions, i.e, solutions containing about 36% to about 70% red cells or fewer. However, as the desirability of administering high hematocrit red cell concentrates has increased, the need for a method and apparatus for depleting leukocytes from these solutions has become apparent.